FIG. 1 is a schematic diagram illustrating structure of frame structure type 1 (referred to as FS1) used in a Long Term Evolution (LTE) Frequency Division Duplexing (FDD) system in related art. In the FDD system, uplink and downlink transmissions use different carrier frequencies. The uplink and downlink transmissions use the same frame structure. On each carrier, one radio frame of which the length is 10 ms contains ten subframes, and the length of each subframe is 1 ms. Each subframe contains two timeslots, and the length of each timeslot is 0.5 ms. A Transmission Time Interval (TTI) of uplink and downlink data transmission is 1 ms.
FIG. 2 is a schematic diagram illustrating structure of frame structure type 2 (referred to as FS2) used in a LTE Time Division Duplex (TDD) system in the related art. In the TDD system, uplink and downlink transmissions use different subframes or different timeslots on the same frequency. In FS2, each radio frame of which the length is 10 ms consists of two half-frames, and the length of each half-frame is 5 ms. Each half-frame contains five subframes, and the length of each subframe is 1 ms. Subframes in FS2 are classified into three types, i.e., a downlink subframe, an uplink subframe, and a special subframe. Each special subframe consists of three parts, i.e., Downlink Pilot Time Slot (DwPTS), Guard Period (GP), and Uplink Pilot Time Slot (UpPTS). The DwPTS may transmit downlink pilot, downlink service data, and downlink control signaling. The GP does not transmit any signal. The UpPTS transmits random access and Sounding Reference Symbol (SRS), and does not transmit uplink service or uplink control information. Each half-frame includes at least one downlink subframe, at least one uplink subframe, and at most one special subframe. Table 1 illustrates seven kinds of uplink-downlink subframe configurations supported by FS2.
TABLE 1Uplink-downlink configurationsDownlink-to-UplinkUplink-Switch-downlinkpointSubframe numberconfigurationperiodicity012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
FIGS. 3A and 3B illustrate structures of data and pilot (i.e., a reference symbols, or a DeModulation Reference Signal (DMRS) for data demodulation) of a LTE Physical Uplink Shared Control Channel (PUSCH) in one subframe. Referring to FIG. 3A, under a conventional Cyclic Prefix (CP), the fourth symbol in each timeslot in each subframe transmits the pilot, and remaining symbols transmit data. Referring to FIG. 3B, under an extended CP, the third symbol in each timeslot in each subframe transmits the pilot, and remaining symbols transmit data. An uplink pilot is a terminal-specific pilot, which is generated according to actual bandwidth size scheduled by the PUSCH. In order to support uplink Multi-User Multiple-Input Multiple-Output (MU-MIMO), each column of pilots may implement orthogonal transmission of pilots of multiple terminals which share the same resources by cyclically shifting the same pilot base sequence. As such, a receiving end may distinguish pilot information of different terminals through cyclic shift.
In a LTE system, channel transmission in the related art is defined in a unit of subframe, and there is not a TTI transmission mechanism which is shorter than 1 ms. Therefore, it is necessary to propose a new DMRS transmission mode to ensure that when multiple TTIs share a DMRS time domain position, the TTIs do not interfere with each other.